Hi Alessandro,
you are referring to an old version of IEM called IEM OS. I believe you are using a new version either IEM Virtual or IEM Pro where there is a different solution.
Please read the whole Identity and access management section for more details. https://docs.eu1.edge.siemens.cloud/get_started_and_operate/industrial_edge_management/operation/iam/01_overview.html
Here is mentioned the email server.
https://docs.eu1.edge.siemens.cloud/get_started_and_operate/industrial_edge_management/operation/iam/verify_email.html
If you would like to reset password of a user of Edge device, the Device Admin can also do it.
Another option is to use the Identity federation of IEM to login to IED. (Check if you have the latest versions of IEM and IED).
https://docs.eu1.edge.siemens.cloud/get_started_and_operate/industrial_edge_management/operation/identity_federation_devices/configuration.html